How does the change in humidity affect my guitar neck?

Discussion in 'Luthier's Corner' started by warmachine, Jan 22, 2011.

  1. warmachine

    warmachine Senior Member

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    I really hate winter and it's now to the point where the temp will be dropping from mid 20's down to the teens! :(

    Right now the majority of my place is at 20% humidity, but I have been able to get one room a consistent 40%+ and this is where I've placed my guitars out on stands.

    What I'm wondering is how does this change in humidity affect my guitar's neck bow? action? Intonation? etc. Seeing as I just gave all my guitars an extra 20-25% humidity boost.

    Thanks for any insight!
     
  2. bfcg

    bfcg Senior Member

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    It should not effect it much if the neck is finished and the fingerboard is not dried out.
    Prolonged dry spells and dry heat will effect it over time.
    Wood expands and contracts with moisture and the trick is to keep moisture from entering or exiting the wood.
    Acoustic guitars are more effected by humidity changes because the inside of the body is generally not sealed causing tops to collapse and in some cases to crack. Backs and sides may also be effected.
     
  3. warmachine

    warmachine Senior Member

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    Last night I tuned them all to standard tuning (70deg 40%humidity in the room at that point) and now after i woke up the old school heat radiators in my apartment had jumped up things up to 76deg 31% humidity. All my guitars are now reading about -15 to -20 below standard tuning according to my Korg digital tuner.

    Turned radiator off for now.
     
  4. Stephmon

    Stephmon Senior Member

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    The subject could fill a book, but in a nutshell... Materials tend to expand as they are heated and contract as they are cooled. The degree to which they react to changes in temperature depend on their Coefficent of Thermal Expansion (there are some neat materials like ceramics that can be 'tuned' to have zero CTE in a given range of temperatures, but that is another topic). Joining materials with broadly different CTE can cause them to struggle against each other (the bi-metalic strip in a thermostat, or an old blinker actually make use of this 'struggle').
    A guitar, being a physical object, will tend to expand and contract with changes in temperature (truss rod and strings included and with a different CTE than the wood), but the effect is relatively small in wood, compared to changes in its moisture content. The relative humidity of a guitar's environment will also cause expansion and contraction, because of the cellular (sponge-like) composition of wood. Wood can actually contract as the temperature goes up, if the RH goes down (wood gives up moisture) and expand as the temperature goes down, if the RH goes up (wood gains moisture).
    An electric has opportunities to give up moisture, even if it seems well sealed. Truss rod channels, neck pockets and pickup routs are generally unsealed. It is a good practice to keep your instrument in the 40-50% RH. Fortunately, it takes more time for 'core' moisture to transfer (compared to transfer at the surface, which is generally sealed by the guitar's finish) so transporting your guitar from one RH controlled environment to another is reasonably harmless (especially in a good case). Leaving your guitar in the trunk overnight, in the dead of a Midwest winter, not so much. If you are transporting through a temperature extreme, it is good practice to leave the guitar in its case for an hour, before getting it out. This slows the change back to room temperature/RH.
    Symptoms of exposure to extremes of Temperature/RH may include changes in the action, frets loosening and exposing their ends, finish checking (spider lines), headaches, runny nose, etc.
     
  5. xsouldriverx

    xsouldriverx V.I.P. Member

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    keeping it between 40%-55% is ideal especially for hollow guitars. 30% is okay but 20% is low. Some guitars dont move, others move wildly and it creates bumps in the board that cause buzzing and in some cases twisting as well as the frets popping out of the sides.
    As you probably know, keep the guitars away from the radiators and baseboards. Even in a room with good humidity the close exposure will effect the guitars. Temperature is a bit less of a concern. I personally dont like heat that high, not for the guitars, but for myself. it just gets too hot for me.
    Remember: If youre comfortable, the guitars is comfortable.
     

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